The invention pertains to electrorheological (ER) and magnetorheologocial (MR) fluid devices, and more particularly, to a device for changing the viscosity and yield stress of ER and MR fluids and for measuring the change in those parameters.
An electrorheological (ER) fluid is typically a suspension of solid particles in dielectric carrier liquids that undergo a rapid and reversible viscosity transition upon the application of electric fields. This dramatic transition of viscosity is often referred to as the ER effect or sometimes the xe2x80x9cWinslow effect,xe2x80x9d after Willis Winslow (1949) who first reported the phenomenon. The ER effect has not been fully understood but can be described as follows: the external electric field induces electric polarization within each particle relative to the carrier liquid (an electric dipole), and the resulting electrostatic interaction forces between the particles lead to the formation of aggregates aligned in the direction of the field. The presence of these particles aggregates in the flow field causes an increase in the fluid viscosity and a decrease in flow rate. During the past two decades, the ER-related investigations have increased due to the potential applications of the special properties of the ER fluids for the performance improvement of devices such as engine mounts, clutches, brakes, and shock absorbers; for examples, see U.S. Pat. No. 5,088,703 (Takano et al.); U.S. Pat. No. 6,082,715 (Vandermolen); U.S. Pat. No. 5,988,336 (Wendt et al.); U.S. Pat. No. 5,358,084 (Schramm); and U.S. Pat. No. 5,322,484 (Reuter).
Numerous experiments show that ER-fluids are generally visco-plastic fluids. Various rheological models have been proposed (e.g., R. B. Bird, R. C. Amstrong and O. Hassager, xe2x80x9cDynamics of Polymeric Liquidsxe2x80x9d, Vol. 1, Fluid Mechanics, Wiley 1987), and the most often used model under shearing deformation is the Bingham plastic model (also referred to as xe2x80x9clinear viscoplastic modelxe2x80x9d), where the shear stress is given by:
xcfx84=xcfx840+xcexcB{dot over (xcex3)}xe2x80x83xe2x80x83(1)
where {dot over (xcex3)} is the shear rate, xcexcB is the constant Bingham viscosity and xcfx840 is the yield stress induced by the electric field. However, it has been found that yielded ER-fluids may experience shear thinning, i.e., its viscosity decreases gradually with the increase of shear rate. This is probably because the destruction of the internal structure responsible for the yield behavior is a gradual process, during which the resistance to deformation becomes weaker, and is not completed until a high shear stress level is reached. Therefore, the Bingham plastic model may overestimate the true yield stress significantly due to the shear thinning at low shear rates. Wan 1982; O""Brien and Julien 1988.
A Herschel-Bulkley Theological model (also referred to as a non-linear viscoplastic model) seems to be more appropriate in depicting the ER-fluid behavior. This rheological model is empirical, nonetheless the results predicted using this model are often accurate over a wide range of shear rates and are reproducible. The key feature of this rheological model is that when the applied stress is smaller than the yield stress, there is no flow; the material supports a finite stress elastically without flow. For the Herschel-Bulkley model, the elastic strains are taken to be small such that the material is considered to be rigid. Once the applied stress exceeds the yield stress of the material, there is a transition from elastic to plastic behavior and the material behaves like a power-law fluid. This behavior can be interpreted to the microstructure of the fluid; for instance, in some ER fluids under a static/alternating electric field, it is found that electrostatic interactions between the dispersed particles lead to a chain-like structure, indicating a yield stress of the ER fluid. Substantial stresses may be required to break down this structure; the ER fluid will then flow. When the stresses are removed, the chain-like structure reforms.
In simple shear, the constitutive equations for the Herschel-Bulkley fluid are as follows:
{dot over (xcex3)}=0⇄xcfx84 less than xcfx840
{dot over (xcex3)} greater than 0⇄xcfx84=xcfx840+K{dot over (xcex3)}nxe2x80x83xe2x80x83(2)
where xcfx840 is a yield stress, K is a flow consistency, and n is a flow index ranging from 0 to 1 for shear thinning fluid. The upper limit where n=1 corresponds to a Bingham plastic fluid, and K becomes the regular dynamic constant viscosity. It has been shown that xcfx840, i.e., the yield stress increases with the applied electric field strength (E) as xcfx840xe2x88x9dExcex1, where xcex1 assumes values close to 2 for low to moderate field strengths, but often appears to fall below 2 for higher E fields. In this rheological model, the yield stress, the fluid consistency, the flow index which are often referred to as the Herschel-Bulkley parameters should be determined from the measurement.
Much of the same discussion also applies to magnetorheological (MR) fluids except that magnetic fields (B) are applied to the MR field rather than a static/alternating electric fields. An MR fluid is typically a suspension of solid particles in diamagnetic liquids that undergo a rapid and reversible viscosity transition upon the application of magnetic fields. This dramatic transition of viscosity is often referred to as the MR effect. In addition, although it has been shown that yield stress increases with the applied magnetic field strength (B) as xcfx840xe2x88x9dBxcex1, the range for xcex1 is not necessarily close to 2 for low to moderate field strengths, or below 2 for higher field strengths, as is the case for ER fluids, as mentioned previously.
There exist several flow-measuring devices (i.e., rheometers) to measure the ER or MR properties. Those rheometers can be classified into three types: 1) capillary tube type, 2) rotating cylinder type, and 3) falling ball/needle type.1-2 These rheometers produce ER/MR-property data (shear stress etc.,) at a shear rate at a time. Thus, in order to measure the ER/MR property over a range of shear rates, it is necessary to repeat the measurement by varying shear rates. In order to cover a range of shear rates, it is necessary to vary pressure, rotating speed, or the density of the falling object. Such operations make an ER/MR-property measurement system complicated and labor intensive. Therefore, there is a need to develop a new rheometer for ER and MR fluids that is simple and accurate.
In U.S. Pat. No. 6,019,735 (Kensey et al.), which is assigned to the same Assignee, namely Visco Technologies, Inc., of the present invention, there is disclosed a scanning-capillary-tube viscometer for measuring the viscosity of a fluid, e.g., circulating blood of a living being. One of the important features of the scanning-capillary viscometer is that both flow rate and pressure drop at a capillary tube can be determined by fluid level variation with time in a U-type tube system, with a only single fluid level variation measurement required for Newtonian fluids, and a range of fluid level variation measurements required for fluids. In particular, using the U-type tube structure, the fluid is exposed to a pressure differential that causes the fluid to move through the U-tube at a first shear rate. This movement of fluid causes the pressure differential to decrease, thereby subjecting the movement of the fluid to a plurality of shear rates, i.e., decreasing shear rates from the first shear rate.
However, the governing equation and apparatus for the ER/MR-property measurement system are quite different from the scanning-capillary-tube viscometer. Thus, the present invention is a combination of the scanning-capillary-tube viscometer with an ER/MR-property measurement system.
Conventional rheometers utilize moving parts that must be calibrated, tend to wear and eventually must be replaced (e.g., pressure transducers). In addition, many of these rheometers must have test runs repeated in order to cover a range of shear rates, thereby making their use not only cumbersome but expensive.
Therefore, there remains a need for a rheometer that can measure the viscosity over range of shear rates, as well as the yield stress in an absolute zero shear rate range, of ER and MR fluids and which uses no moving parts, including pressure transducers. Furthermore, this rheometer must be simple to use, exhibit quick operation and be comparatively inexpensive.
An apparatus for determining the viscosity of a fluid (e.g., an electrorheological fluid, a magnetorheological fluid, etc.) over plural shear rates using a decreasing pressure differential. The apparatus comprises: a fluid source elevated at a first reference position above a horizontal reference position; a flow restrictor (e.g., a slit or capillary tube) having a first end and a second end and wherein the first end is in fluid communication with the fluid source and wherein the flow restrictor has some known dimensions; a lumen (e.g., a transfer tube) having one end in fluid communication with the second end of the flow restrictor and another end that is exposed to atmospheric pressure and wherein the lumen has a portion (e.g., a riser tube) that is positioned at an angle greater than zero degrees with respect to the horizontal reference position, and wherein a pressure differential exists between a column of fluid in the portion and the elevated fluid source; and whereby the column of fluid moves through the flow restrictor and the lumen at a first shear rate caused by the pressure differential; and whereby the movement of fluid causes the pressure differential to decrease from the first shear rate for generating the plural shear rates; a sensor (e.g., a light array/charge coupled device) for detecting the movement of the column of fluid and wherein the sensor generates data relating to the movement of the column of fluid over time; an electric/magnetic field generator for subjecting said flow restrictor to an electric/magnetic field (e.g., a static electric field, an alternating electric field, a static magnetic field, or an alternating magnetic field, etc.) when the fluid is flowing therein; and a processor, coupled to the sensor, for calculating the viscosity of the fluid over a range of plural shear rates based on the data relating to the movement of the column of fluid over time and the some known dimensions.
In accordance with another aspect of the invention, another apparatus is provided for determining the viscosity of a fluid (e.g., an electrorheological fluid, a magnetorheological fluid, etc.) over plural shear rates using a decreasing pressure differential. The apparatus comprises: a fluid source elevated at a first reference position above a horizontal reference position; a valve in fluid communication with the fluid source via a first port for controlling a flow of fluid from the fluid source; a flow restrictor (e.g., a slit or capillary tube) having a first end and a second end wherein the first end is in fluid communication with a second port of the valve and wherein the flow restrictor has some known dimensions and is positioned at the horizontal reference position; a lumen (e.g., a riser tube) having one end in fluid communication with a third port of the valve and another end that is exposed to atmospheric pressure and wherein the lumen is positioned at an angle greater than zero degrees with respect to the horizontal reference position; a processor coupled to the valve for controlling the valve to permit the flow of fluid into the lumen to form a column of fluid therein whereby a pressure differential is formed between a level of the column of fluid and the flow restrictor; the processor is also arranged for operating the valve to isolate the lumen from the fluid source and for coupling the flow restrictor and the lumen together to generate a falling column of fluid in the lumen; and whereby the falling column of fluid moves through the lumen, through the valve and the flow restrictor at a first shear rate caused by the pressure differential and wherein the movement of fluid causes the pressure differential to decrease from the first shear rate for generating the plural shear rates; a sensor (e.g., a light array/charge coupled device) for detecting the movement of the falling column of fluid and wherein the sensor generates data relating to the movement of the falling column of fluid over time; an electric/magnetic field generator for subjecting the flow restrictor to an electric/magnetic field (e.g., a static electric field, an alternating electric field, a static magnetic field or an alternating magnetic field, etc.) when the fluid is flowing therein; and wherein the processor, also coupled to the sensor, calculates the viscosity of the fluid over a range of plural shear rates based on the data relating to the movement of the falling column of fluid over time and the some known dimensions.
In accordance with another aspect of this invention, another apparatus is provided for determining the viscosity of a fluid (e.g., an electrorheological fluid, a magnetorheological fluid, etc.) over plural shear rates using a decreasing pressure differential. The apparatus comprises: a fluid source elevated at a first reference position above a horizontal reference position; a valve in fluid communication with the fluid source via a first port for controlling a flow of fluid from the fluid source, wherein the valve comprises a second port having a first lumen (e.g., a transfer tube) coupled thereto, and wherein the first lumen has a portion positioned at the horizontal reference position; a flow restrictor (e.g., a slit or capillary tube) having a first end and a second end, wherein the first end is in fluid communication with a third port of the valve and wherein the flow restrictor has some known dimensions; a second lumen (e.g., a riser tube) having one end in fluid communication with a said second end of the flow restrictor and another end that is exposed to atmospheric pressure, wherein the second lumen is positioned at an angle greater than zero degrees with respect to the horizontal reference position, and wherein the flow restrictor and the valve are located at a position below the horizontal reference position; a processor coupled to the valve for controlling the valve to permit the flow of fluid into the flow restrictor and the second lumen to form a column of fluid therein whereby a pressure differential is formed between a level of the column of fluid and the portion of the first lumen, wherein the processor is also arranged for operating the valve to isolate the flow restrictor and the second lumen from the fluid source and for coupling the flow restrictor and the second lumen to the first lumen to generate a falling column of fluid in the second lumen and the flow restrictor, wherein the falling column of fluid moving through the second lumen, through the flow restrictor, through the valve and through the first lumen at a first shear rate caused by the pressure differential, and wherein the movement of fluid causes the pressure differential to decrease from the first shear rate for generating the plural shear rates; a sensor (e.g., a light array/charge coupled device) for detecting the movement of the falling column of fluid, wherein the sensor generates data relating to the movement of the falling column of fluid over time; an electric/magnetic field generator for subjecting the flow restrictor to an electric/magnetic field (e.g., a static electric field, an alternating electric field, a static magnetic field, or an alternating magnetic field) when the fluid is flowing therein; and the processor, also coupled to the sensor, for calculating the viscosity of the fluid over a range of plural shear rates based on the data relating to the movement of the falling column of fluid over time and the some known dimensions.
In accordance with another aspect of this invention, another apparatus is provided for determining the viscosity of a fluid (e.g., an electrorheological fluid, a magnetorheological fluid, etc.) over plural shear rates using a decreasing pressure differential. The apparatus comprises: a fluid source elevated at a first reference position above a horizontal reference position; a valve in fluid communication with the fluid source via a first port for controlling a flow of fluid from the fluid source and wherein the valve further comprises a second port that is exposed to atmospheric pressure; a flow restrictor (e.g., a slit or capillary tube) having a first end, said flow restrictor having some known dimensions and being positioned at said horizontal reference position; a lumen (e.g., a riser tube) having one end in fluid communication with a third port of the valve and another end that is in fluid communication with the first end of the flow restrictor wherein the lumen is positioned at an angle greater than zero degrees with respect to the horizontal reference position; a processor coupled to the valve for controlling the valve to permit the flow of fluid into the lumen to form a column of fluid therein whereby a pressure differential is formed between a level of the column of fluid and the flow restrictor; the processor is also arranged for operating the valve to isolate the lumen from the fluid source and for coupling the lumen to the third port to generate a falling column of fluid in the lumen, wherein the falling column of fluid moves through the lumen and through the flow restrictor at a first shear rate caused by the pressure differential, and wherein the movement of fluid causes the pressure differential to decrease from the first shear rate for generating the plural shear rates; a sensor (e.g., a light array/charge coupled device) for detecting the movement of the falling column of fluid and wherein the sensor generates data relating to the movement of the falling column of fluid over time; an electric/magnetic field generator for subjecting said flow restrictor to an electric/magnetic field (e.g., a static electric field, an alternating electric field, a static magnetic field, or an alternating magnetic field) when the fluid is flowing therein; and the processor, also coupled to the sensor, for calculating the viscosity of the fluid over a range of plural shear rates based on the data relating to the movement of the falling column of fluid over time and the some known dimensions.
In accordance with another aspect of this invention, a method is set forth for determining the viscosity of a fluid (e.g., an electrorheological fluid, a magnetorheological fluid, etc.) over plural shear rates using a decreasing pressure differential. The method comprises the steps of: (a) elevating a fluid source above a horizontal reference position to establish a pressure differential between the fluid source and the horizontal reference position; (b) placing one end of a flow restrictor (e.g., a slit or capillary) in fluid communication with the fluid source and wherein the flow restrictor comprises some known parameters; (c) placing a second end of the flow restrictor in fluid communication with one end of a lumen (e.g., a riser tube) and wherein a second end of the lumen is exposed to atmospheric pressure; (d) positioning the lumen at angle greater than zero degrees with respect to the horizontal reference position; (e) allowing the fluid to flow from the fluid source through the flow restrictor and the lumen, thereby decreasing the pressure differential which causes the fluid to experience a plurality of shear rates; (f) applying an electric/magnetic field (e.g., a static electric field, an alternating electric field, a static magnetic field, or an alternating magnetic field) to the flow restrictor as the fluid flows through the flow restrictor (g) detecting the movement of the fluid through the lumen over time to generate data relating to the movement of the fluid through the lumen; and (h) calculating the viscosity of the fluid over a range of shear rates based on the data and the some known parameters.
In accordance with another aspect of this invention, another method is set forth for determining the viscosity of a fluid (e.g., an electrorheological fluid, a magnetorheological fluid, etc.) over plural shear rates using a decreasing pressure differential. The method comprises the steps of: (a) elevating a fluid source above a horizontal reference position and disposing the fluid source in fluid communication with a first port of a valve; (b) disposing one end of a lumen (e.g., a riser tube) in fluid communication with a second port of said valve with the other end of said lumen exposed to atmospheric pressure, said lumen being positioned at an angle greater than zero degrees; (c) disposing one end of a flow restrictor (e.g., a slit or capillary tube) in fluid communication with a third port of the valve at the horizontal reference position and wherein the flow restrictor comprises some known parameters; (d) operating the valve to couple the first port with the second port to generate a column of fluid of a predetermined length in the lumen, and wherein the column of fluid of predetermined length establishes a pressure differential between the column of fluid and the horizontal reference position; (e) operating the valve to decouple the second port from the first port and to couple the second port with the third port to generate a falling column of fluid in the lumen, thereby decreasing the pressure differential which causes the fluid to experience a plurality of shear rates; (f) applying an electric/magnetic field (e.g., a static electric field, an alternating electric field, a static magnetic field, or an alternating magnetic field) to the flow restrictor as the fluid flows through the flow restrictor; (g) detecting the movement of the fluid through the lumen over time to generate data relating to the movement of the fluid through the lumen; and (h) calculating the viscosity of the fluid over a range of shear rates based on the data and the some known parameters.
In accordance with another aspect of this invention, another method is set forth for determining the viscosity of a fluid (e.g., an electrorheological fluid, a magnetorheological fluid, etc.) over plural shear rates using a decreasing pressure differential. The method comprises the steps of: (a) elevating a fluid source above a horizontal reference position and disposing the fluid source in fluid communication with a first port of a valve; (b) disposing one end of a flow restrictor (e.g., a slit or capillary tube), having some known parameters, in fluid communication with a second port of the valve with the other end of the flow restrictor being in fluid communication with one end of a first lumen (e.g., a riser tube) and wherein the first lumen has another end exposed to atmospheric pressure, and wherein the first lumen is positioned at an angle greater than zero degrees with respect to the horizontal reference position; (c) positioning the flow restrictor and the valve below the horizontal reference position and coupling a third port of the valve with a second lumen (e.g., transfer tube) and wherein a portion of the second lumen is disposed at the horizontal reference position; (d) operating the valve to couple the first port with the second port to generate a column of fluid of a predetermined length in the flow restrictor and the first lumen and wherein the column of fluid of a predetermined length establishes a pressure differential between the column of fluid and the horizontal reference position; (e) operating the valve to decouple the second port from the first port and to couple the second port with the third port to generate a falling column of fluid in the flow restrictor and the first lumen, thereby decreasing the pressure differential which causes the fluid to experience a plurality of shear rates; (f) applying an electric/magnetic field (e.g., a static electric field, an alternating electric field, a static magnetic field, or an alternating magnetic field) to the flow restrictor as the fluid flows through the flow restrictor; (g) detecting the movement of the fluid through the the first lumen over time to generate data relating to the movement of the fluid through said first lumen; and (h) calculating the viscosity of the fluid over a range of shear rates based on the data and the some known parameters.
In accordance with another aspect of this invention, another method is set forth for determining the viscosity of a fluid (e.g., an electrorheological fluid, a magnetorheological fluid, etc.) over plural shear rates using a decreasing pressure differential. The method comprises the steps of: (a) elevating a fluid source above a horizontal reference position to establish a pressure differential between the fluid source and the horizontal reference position, and disposing the fluid source in fluid communication with a first port of a valve; (b) disposing one end of a lumen (e.g., a riser tube) in fluid communication with a second port of the valve with the other end of said lumen being in fluid communication with a flow restrictor (e.g., a slit or capillary tube) disposed at the horizontal reference position and wherein the flow resistor comprises some known parameters and wherein the lumen is positioned at an angle greater than zero degrees with respect to the horizontal reference position; (c) positioning a third port of the valve to be exposed to atmospheric pressure; (d) operating the valve to couple the first port with the second port to generate a column of fluid of a predetermined length in the lumen; (e) operating the valve to decouple the second port from the first port and to couple the second port with the third port to generate a falling column of fluid in the lumen, thereby decreasing the pressure differential which causes the fluid to experience a plurality of shear rates; (f) applying an electric/magnetic field (e.g., a static electric field, an alternating electric field, a static magnetic field, or an alternating magnetic field) to the flow restrictor as the fluid flows through the flow restrictor; (g) detecting the movement of the fluid through the lumen over time to generate data relating to the movement of the fluid through the lumen; and (h) calculating the viscosity of the fluid over a range of shear rates based on the data and the some known parameters.